When orange-brown copper metal is added to a colourless solution of silver nitrate, the copper displaces the silver. This causes two colour changes:
It's a measure of how fast the reactants are being used up or how fast the products are being formed.
Increasing temperature increases the rate of reaction. Particles gain more kinetic energy, move faster, and collide more frequently and with more energy.
Increasing concentration (for solutions) or pressure (for gases) increases the rate. There are more reactant particles in the same volume, leading to more frequent collisions.
Increasing the surface area (e.g., using a powder instead of a lump) increases the rate. More particles are exposed, leading to more frequent collisions.
A substance that increases the rate of reaction and remains chemically unchanged at the end. It provides an alternative reaction pathway with a lower activation energy.
Enzymes are biological catalysts. Iron is a catalyst in the Haber process.
Some chemical reactions require light energy to happen. These are called photochemical reactions.
Increasing the light intensity increases the rate of these reactions. Examples include photosynthesis and the decomposition of silver halides.
For a reaction to occur, reactant particles must collide. But not just any collision will do!
The colliding particles must have enough energy. This minimum energy is called the Activation Energy (Ea).
The colliding particles must have the correct orientation (they must face each other in the right way).
The rate of reaction depends on the frequency of successful collisions.
We can measure the rate by tracking changes in gas volume, mass, or the formation of a precipitate.
Example Reaction: Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
Example Reaction: CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
Example Reaction: Na2S2O3(aq) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + SO2(g) + S(s)
To find the rate at a particular time, you need to find the gradient of the curve at that point.
The reaction between Iodine and methanoic acid produces carbon dioxide gas. The rate can be found by plotting volume of CO2 vs. time.
I2(aq) + HCOOH(aq) → 2I-(aq) + 2H+(aq) + CO2(g)
To calculate the rate of reaction at 20 seconds: